1. Field of the Invention
The present invention relates to a table moving apparatus for use with the semiconductor manufacturing or super precision processing apparatus and more particularly, it relates to a table moving apparatus including a table having a plane kept horizontal and movable in the vertical direction.
2. Description of the Related Art
A circuit pattern formed on the mask (or reticule) is projected and exposed on wafers through the projection lens in the course of manufacturing semiconductors. In order to accurately project the circuit pattern on wafers, it is needed that the table on which the wafers are chucked is positioned at a predetermined position with high accuracy. More specifically, the table moving apparatus has X, Y and Z tables 1, 2 and 3 which move in directions X, Y and Z, respectively, as shown in FIG. 1, for the purpose of positioning the wafer table (not shown) in the horizontal direction (or directions X and Y which are perpendicular to each other) and in the vertical direction (or direction Z). Z table 3 is mounted on Y table 2 and the wafer table (not shown) is mounted on Z table 3.
Z table is moved relative to Y table in direction Z by the Z table moving mechanism which will be described later. Ring-shaped member 4 which encloses axial line Z and rotates round it is mounted on Y table 2. Three wedge-like blocks 5 each having a tapered face are fixed on the upper horizontal face of ring-shaped member 4 with same interval interposed between the adjacent ones in the circumferential direction of member 4. Bearing ball 6 is arranged on the tapered face of each of wedge-like blocks 5 and Z table 3 is mounted on these bearing balls 6. When ring-shaped member 4 rotates round axial line Z to move wedge-like blocks 5 in the horizontal direction, therefore, balls 6 slide up and down on their respective tapered faces. Z table 3 is thus moved in the vertical direction or in direction Z.
In the case of the Z table moving mechanism shown in FIG. 1, ring-shaped member 4, wedge-like blocks 5 and ball bearings 6 are mounted in this order on Y table 2. Z table 3 on Y table 2 is thus made elevated relatively high. This is a first problem. The more elevated Z table 3, the greater the inertia with which X table 1 moves in direction X, or Y table 2 moves in direction Y. The greater this inertia, the more difficult it will be to position Z table 3 accurately in respect to both direction X and direction Y.
That face of Z table 3 on which something like the wafer is placed is essentially kept horizontal. When this face of Z table 3 is slanted from the horizontal plane, therefore, it is deemed that error is caused. In other words, when this face of Z table 3 is slanted from the horizontal plane and swung round axial line X, it is deemed that pitching error is caused, while when it is swung round axial line Y, it is deemed that rolling error is caused. When these errors are caused, the following disadvantage arises. When that face of Z table 3 on which something like the wafer is mounted is located at an exact position and kept horizontal, the projection lens can be focused all over the wafer on the face of Z table 3, When the face of Z table 3 is located at the exact position but not kept horizontal and slanted from the horizontal plane, however, the projection lens can be focused not all over the wafer but only onto a part thereof. As the result, the circuit pattern on the mask cannot be accurately projected and exposed on the remaining part of the wafer on which the projection lens cannot be focused.
It is difficult in the case of the Z table moving mechanism shown in FIG. 1 that the tapered face of the wedge-like block is processed with high accuracy. When this tapered face is neither excellent in its flatness nor formed to have such exact an angle as previously determined, Z table cannot be move in accordance with the movement of ring-shaped member. When the flatness and angle of the tapered face of one wedge-like block is different from those of the other two, for example, Z table is moved up and down, slanting from the horizontal plane, and pitching or rolling error is thus caused. This is a second problem.
The term "resolution" will be used in this specification. An object can move every 10 .mu.m but another object can move only every 1000 .mu.m. The former which can move delicately has high or good resolution, while the latter which can move roughly has low or bad resolution. Heedless to say, positioning can be achieved with high accuracy in the case of the former and it can be achieved with low accuracy in the case of the latter.
When the tapered surface is not sufficiently smooth, or when the vertical movement of the bearing balls 6 is not proportional to that of the wedge-likes blocks 6, balls 6 cannot move but in a low resolution.
As the result, the resolution of Z table is low or bad and the accuracy of its positioning is low. This is a third problem.
Another Z table moving mechanism is intended to tilt Z table so as to correct the tilt of that face of Z table on which something like the wafer is mounted. As shown in FIG. 2, lift means 7 is interposed between ring-shaped member 4 and each of wedge-like blocks 5. When one of lift means 7 is driven, therefore, Z table 3 is lifted at one of those points thereof where Z table 3 is mounted on ball bearings 6, thereby causing Z table 3 to be tilted. However, the height of Z table 3 on Y table 2 is made higher only by the height of lift means 7 than that of Z table 3 on Y table 2 in the mechanism shown in FIG. 1. In addition, pitching error and the like are likely to be caused even in the table moving mechanism shown in FIG. 2 because of the reasons mentioned relating to the mechanism shown in FIG. 1.
The table moving mechanism which is intended to tilt Z table may be provided with three actuators 8, as shown in FIG. 3. Each of actuators 8 includes slider member 9 extended in the vertical direction and slidable in the same direction to lift Z table. When three actuators 8 are driven at the same time, Z table 3 is moved up and down in the vertical direction and when one of actuators 8 is driven, that face of Z table 3 on which the wafer or the like is mounted is tilted. However, it is needed that each of the actuators has slider member 9 which is extended and slidable in the vertical direction. The height of Z table 3 on Y table 2 is thus made relatively high.
Slider members 9 of the actuators in the table moving mechanism shown in FIG. 3 may be moved by feed screw means or piezo-electric elements. In the case where slider members 9 are moved by the feed screw means, their range in which they can move is large but they can move only roughly (or their resolution is low or bad). The movable range of Z table is thus made large but its resolution is low or bad and the accuracy of positioning it is low accordingly. This is the above-mentioned third problem.
In the other case where slider members 9 are moved by the piezo-electric elements, they can be moved extremely delicately (or their resolution is high or good), but their movable range is relatively small. Z table can be thus moved with high accuracy but its movable range is small. This is a fourth problem.